Measuring the dynamical status of the evolving galaxy clusters
Abstract
The formation of galaxy clusters is not a unique process. Due to the assembling by mergers and accretions, together with a continuous quest to reach dynamical equilibrium by virialization, it is more a sequence of unrelaxed/relaxed states. Measuring the current dynamical status of a specific cluster (or future cluster) is, thus, a hard job, and although there are many ways to treat the problem, a physically motivated method that is simple on its conception and robust on its results is still lacking. Our proposal is to quantify the degree of evolution of galaxy systems, from their observed global properties, by means of the evolution of their entropy. It is expected that the evolution towards relaxation corresponds to an increase in entropy. In the case of isolated systems, the virialization is a state of maximum entropy. When the system is not isolated, the sequence of mergers and accretions generate new entropy maxima. Since the thermodynamical behavior of self-gravitating systems is much peculiar, conventional thermodynamical expressions do not work entirely. In this work, we present a formalism that modifies some of such expressions to include gravitational systems. Specifically, entropy is first calculated as a function of the virial mass, velocity dispersion and volume. In a validation process we also use entropy measurements based on the information theory, considering the radial, azimuthal and line-of-sight distribution of galaxies in the cluster. This method was applied to a sample of 70 galaxy clusters in the Local Universe, well sampled and studied, and the results correlate very well with different previous estimations of dynamical status for these systems.
- Publication:
-
Galaxy Cluster Formation II
- Pub Date:
- June 2021
- DOI:
- 10.5281/zenodo.5007389
- Bibcode:
- 2021gcf2.confE..72Z
- Keywords:
-
- Zenodo community gcf2021;
- Entropy;
- dynamical relaxation